Kraft Paper GSM and BF Explained: How to Choose the Right Grade

Every kraft paper enquiry we receive comes down to two numbers: GSM and BF. Get them right and the rest of the order is straightforward. Get them wrong and you either pay for strength you do not need, or your boxes fail in transit.

Here is what the two numbers mean and how to pick a combination.

What GSM measures

GSM is grams per square metre — the weight of one square metre of the paper. It is a measure of substance, not strength, though the two are related.

Low GSM (80–100) — light wrapping, inner liners, low-cost cartons
Medium GSM (100–150) — the working range for most corrugated boxes
High GSM (150–200+) — heavy-duty outers, export cartons, industrial packaging

A higher GSM sheet contains more fibre per square metre, so it is generally stiffer and heavier. It also costs more per tonne of finished box, which is why over-specifying is a common and expensive mistake.

What BF measures

BF is the burst factor — resistance to bursting pressure, normalised against the paper's weight. It is the number that tells you how much punishment the paper takes before it ruptures.

Because BF is already adjusted for weight, a 16 BF sheet at 120 GSM and a 16 BF sheet at 180 GSM have comparable strength per unit of substance. The heavier sheet is stronger in absolute terms, but the fibre quality is similar.

This is the part buyers most often misread. Asking for "the strongest kraft" usually means asking for a higher BF, not simply a higher GSM.

Reading the two together

Application	Typical GSM	Typical BF
Inner liners, light wraps	80 – 100	12 – 16
Standard corrugated boxes	100 – 150	16 – 20
Heavy-duty and export cartons	150 – 200	18 – 24
Industrial and specialty	200+	20 – 28

Treat these as starting points, not rules. The right grade depends on what goes inside the box, how far it travels, how it is stacked and whether it will sit in humidity.

Where the shade fits in

Kraft is supplied in natural shade and golden yellow. The difference is largely cosmetic — golden yellow carries a warmer, more uniform tone that prints cleanly and looks better on a retail-facing box. Natural shade is the default for industrial use where appearance does not matter.

Shade does not change strength. If a supplier quotes a strength difference between shades, ask what is actually different about the furnish.

Three practical checks before you order

Match BF to the load, GSM to the format. Heavy contents need burst resistance; large panels need substance.
Ask for the reel width you actually run. Slitting waste is real money at tonne volumes.
Test a small lot first on a new grade. Especially when switching supplier or moving between virgin and recycled furnish.

Common mistakes

Over-specifying GSM to compensate for low BF. You end up paying for weight that does not solve the failure mode. Raise the BF instead.

Ignoring moisture. Paper loses strength as it picks up humidity. If your godown is damp or the shipment crosses a monsoon route, build in margin.

Quoting only GSM. A quote without a BF figure is not a quote for a specific grade. Always state both.

If you know your GSM and BF and want pricing on a bulk lot, send us the specification along with quantity and delivery city. If you are not sure which grade fits, tell us what you are packing and we will suggest one.